Wall-clock source, in epoch milliseconds. Defaults to Date.now.

This is the one place in the package that reads a clock directly, and the deviation from AI_GUIDELINES §4.2 is deliberate: a Durable Object is constructed by the platform as (state, env), with no plugin context and therefore no route to IRuntimeServices. This class IS the runtime boundary for the object, in the same sense packages/runtime is for a Worker. Injecting the seam is what keeps expiry testable without waiting.